I don't quite get Arcor's reaction. They are a common carrier after all, no? Can a company force phone companies to disconnect a competitor over uncompetitive behaviour? I don't think so.

Arcor folding opens a can of worms for all kind of demands not only against them but against any ISP.

(Update: German Spreeblick reports that Arcor themselves sell adult video-on-demand services... seems quite a few participants in this are conflicted in their decisions!)

I agree with Martin. ISPs should not be doing this.

Blocking can be defeated very easily through the use of proxies.

Update: Gee. Turns out Arcor's "filter" blocked perfectly harmless websites of scientific conferences (Industrial Ethernet Congress, whose website was on the same server as Privateamateure.com, one of the censored sites) and companies (Siemens and more). They disabled the filter now, which worked on IP and not domain basis, having a "collateral damage" of blocking 3,5 million websites, Spiegel reports. The *actual porn* sites in the meantime had changed their IP addresses... escaping the block!

http://www.spiegel.de/netzwelt/web/0,1518,506143,00.html